On Tue, 2007-02-20 at 20:19 +0530, Ritesh Raj Sarraf wrote: > Luca Berra wrote: > > > i meant that LVM (actually device-mapper) does not do anything special. > > it just passes the IO requests from the fs layer to the > > underlying block device and if the underlyng block device returns an IO > > error then it is passed back to the fs. which will cause ext2 to remount > > the filesystem readonly. > > Hi, > > Thanks for clarifying. > > In my case, the block device is hidden by the multipathing layer. > It is something like: > (Block Device(Multipathing(LVM(Filesystem) ) ) ) > > Now during takeover/giveback, the multipathing layer is intelligent enough to > wait till <120 seconds before declaring that the path has really gone offline > and no more paths are available. > If within the 120 seconds time span, the takeover succeeds, the path is back > online and everything works fine in a non-LVM setup. > > It is only in an LVM setup that a takeover/giveback ends up with the host OS > having a filesystem read-only problem. Interesting. > Now if I go with your explanation, I shouldn't have had the filesystem read-only > problem since the I/O is being passed on to the multipathing layer which is > intelligent enough to wait for N seconds before really sending an I/O Error. > > Are there any timeout options in LVM to allow it to wait for N seconds before > sending out an error ? > (I understand that LVM might not be involved, but just wondering). > There are no LVM timeouts like you are suggesting. LVM just does I/O to devices like any other application. The timeout settings you're looking for should be in the layers below LVM. What does your /etc/multipath.conf file look like? Do you have "no_path_retry" set and/or "queue_if_no_path"? Both of these settings will affect how multipath deals with a "no paths available" situation. There are also settings below multipath, in the low-level driver(s). Since you are using iscsi, I assume you've got open-iscsi? You can set node.session.timeo.replacement_timeout to a lower value (it is 120 by default in /etc/iscsi/iscsid.conf) if you want faster path failure detection and faster failover. In a lot of cases, people set the low level driver timeouts smaller (< 30 sec) to allow for quicker failure detection and failover, but a higher or infinite value for the "no paths available" situation. You might try open-iscsi.org and/or dm-devel lists. > > Thanks, > Ritesh _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
